crossover frequency c/lfe via vt1708s center channel

[babosa70]

I am building an HTPC with an ASUS M4A785-M motherboard via vt1708s on-board sound. will be 7.1 using this via chip. the analog orange colored jack is one mono channel for center speaker and one mono channel for sub woofer. I suspect that the sub woofer channel frequency response range is 20hz - 80hz and the center channel frequency response range is 80hz - 20khz but I have been unable to confirm this after searching all over the Internet and carefully reading the via specifications. Getting a new motherboard or an add on sound card with known specs is not a viable solution for me.

Could it be that there is some overlap between the frequency response of the c/lfe (Center / Low Frequency Effects) channels?

a theoretical example of what i mean by overlap might be that the sub-woofer channel range was 20hz to 120hz and the center channel range was 100hz to 20khz. Theoretically a 20hz overlap

Thanks in advance


Carlos

 

[americanaudiophile]

There is always overlap.
When they give the sub crossover as 80hz that means that the level is 3db down at this frequency. Depending on the crossover order (2 or 3)or slope (12 or 18db/octave) you may still hear output as high as 3 octaves higher than this (about 300hz).
The frequency range of the speakers themselves are added to the effects of the crossover.
The crossover settings in surround sound systems are designed to allow 5 or 7 full range channels plus LFE bass .1 channel to be encoded in the video and let the surround processor limit the output of those speakers that are not capable of handling bass and redirect it to those that can handle it (usually the sub but sometimes L/R front and sub).
80hz is the default crossover frequency (taken from THX specs). Many satellites speakers don't go that low so benefit from a higher crossover (100-120 hz). If you go higher than that that on the subwoofer it starts to become directional which is not good. That's why a lot a sat sub setup have a gap in the bass that you can't really do anything about.

 

[jsmithepa]

Look for control panel setting Large=No Crossover/full range, Small=Yes Crossover.

Buying a sound card just for this "imperfection?" maybe a little over the top. As already mentioned, there are always some overlap. If it bothers you that much, how about a nice inline high pass filter like THIS?

 

[babosa70]

There is always overlap.
When they give the sub crossover as 80hz that means that the level is 3db down at this frequency. Depending on the crossover order (2 or 3)or slope (12 or 18db/octave) you may still hear output as high as 3 octaves higher than this (about 300hz).
The frequency range of the speakers themselves are added to the effects of the crossover.
The crossover settings in surround sound systems are designed to allow 5 or 7 full range channels plus LFE bass .1 channel to be encoded in the video and let the surround processor limit the output of those speakers that are not capable of handling bass and redirect it to those that can handle it (usually the sub but sometimes L/R front and sub).
80hz is the default crossover frequency (taken from THX specs). Many satellites speakers don't go that low so benefit from a higher crossover (100-120 hz). If you go higher than that that on the subwoofer it starts to become directional which is not good. That's why a lot a sat sub setup have a gap in the bass that you can't really do anything about.

 

[babosa70]

Sr. (Sra.?) americanaudiophile,

Extreme thank you for this valuable information (priceless for me) Since you posses this very specific information mixed with lots of other knowledge you probably neither realize how valuable it could be to some individuals nor how clear and concise you explanation is. and how difficult it is to find.

Thanks again obrigadão

Carlos in central Brasil